CLAT PG - Compressors, Gas Turbines & Jet Engines 1000+ MCQ [Solved] PDF Download

1. The compressor efficiency is the
A. Isothermal H.P/indicated H.R
B. Isothermal H.P./shaft H.R
C. Total output/air input
D. Compression work/motor input
Answer : A

2. Isothermal compression efficiency, even when running at high speed, can be approached by using
A. Multistage compression
B. Cold water spray
C. Both (A) and (B) above
D. Fully insulating the cylinder
Answer : C

3. The ratio of work done per cycle to the swept volume in case of compressor is called
A. Compression index
B. Compression ratio
C. Compressor efficiency
D. Mean effective pressure
Answer : D

4. Reheating in a gas turbine
A. Increases the thermal efficiency
B. Increases the compressor work
C. Increases the turbine work
D. Decreases the thermal efficiency
Answer : A

5. In open cycle turbojet engines used in military aircraft, reheating the exhaust gas from the turbine by burning, more fuel is used to increase the
A. Thrust and range of aircraft
B. Efficiency of the engine
C. Both (A) and (B)
D. None of these
Answer : A

6. The mean effective pressure of the compressor is the
A. Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
B. Volume of air delivered by the compressor
C. Volume of air sucked by the compressor during its suction stroke
D. None of the above
Answer : D

7. Efficiency of gas turbine is increased by
A. Reheating
B. Inter cooling
C. Adding a regenerator
D. All of the above
Answer : C

8. The maximum propulsion efficiency of a turbojet is attained at around following speed
A. 550 km/hr
B. 1050 km/hr
C. 1700 km/hr
D. 2400 km/hr
Answer : D

9. In the axial flow gas turbine, the work ratio is the ratio of
A. Compressor work and turbine work
B. Output and input
C. Actual total head temperature drop to the isentropic total head drop from total head inlet to static head outlet
D. Actual compressor work and theoretical compressor work
Answer : C

10. Maximum work is done in compressing air when the compression is
A. Isothermal
B. Adiabatic
C. Polytropic
D. None of the above
Answer : B

11. Separators in compressor installations are located
A. Before intercooler
B. After intercooler
C. After receiver
D. Between after-cooler and air receiver
Answer : D

12. Which is false statement about multistage compression?
A. Power consumption per unit of air delivered is low
B. Volumetric efficiency is high
C. It is best suited for compression ratios around 7:1
D. The moisture in air is condensed in the intercooler
Answer : B

13. The pressure ratio in gas turbines is of the order of
A. 2 : 1
B. 4 :1
C. 61 : 1
D. 9 : 1
Answer : C

14. The volume of air sucked by the compressor during its suction stroke is called
A. Free air delivery
B. Compressor capacity
C. Swept volume
D. None of these
Answer : C

15. Reciprocating air compressor is best suited for
A. Large quantity of air at high pressure
B. Small quantity of air at high pressure
C. Small quantity of air at low pressure
D. Large quantity of air at low pressure
Answer : A

16. In gas turbines, high thermal efficiency is obtained in
A. Closed cycle
B. Open cycle
C. Both of the above
D. Closed/open depending on other considerations
Answer : A

17. The ratio of isentropic work to Eulers work is known as
A. Compressor efficiency
B. Isentropic efficiency
C. Euler's efficiency
D. Pressure coefficient
Answer : D

18. The indicated work per unit mass of air delivered is
A. Directly proportional to clearance volume
B. Greatly affected by clearance volume
C. Not affected by clearance volume
D. Inversely proportional to clearance volume
Answer : C

19. Reheating in gas turbine results in
A. Increase of work ratio
B. Decrease of thermal efficiency
C. Decrease of work ratio
D. Both (A) and (B) above
Answer : D

20. The overall isothermal efficiency of the compressor is defined as the ratio of
A. Work required to compress the air isothermally to the actual work required to compress the air for the same pressure ratio
B. Isothermal power to the shaft power or B.P. of the motor or engine required to drive the compressor
C. Volume of free air delivery per stroke to the swept volume of the piston
D. Isentropic power to the power required to drive the compressor
Answer : B

21. In jet engines, paraffin is usually used as the fuel because of its
A. Highcalorific value
B. Ease of atomisation
C. Low freezing point
D. Both (A) and (C) above
Answer : D

22. For minimum work in multistage compression, assuming same index of compression in all stages
A. Work done in first stage should be more
B. Work done in subsequent stages should increase
C. Work done in subsequent stages should decrease
D. Work done in all stages should be equal
Answer : D

23. Mechanical efficiency of gas turbines as compared to I.C engines is
A. Higher
B. Lower
C. Same
D. None of the above
Answer : A

24. The air-fuel ratio in gas turbines is of the order of
A. 7 : 1
B. 15 : 1
C. 30 : 1
D. 50 : 1.
Answer : D

25. The volumetric efficiency of a compressor
A. Increases with decrease in compression ratio
B. Decreases with decrease in compression ratio
C. Increases with increase in compression ratio
D. Decreases with increase in compression ratio
Answer : D

26. The maximum delivery pressure in a rotary air compressor is
A. 10 bar
B. 20 bar
C. 30 bar
D. 50 bar
Answer : A

27. After-cooler is used to
A. Cool the air
B. Decrease the delivery temperature for ease in handling
C. Cause moisture and oil vapour to drop out
D. Reduce volume
Answer : C

28. It is not possible to use closed gas turbine cycle in aeronautical engines because
A. It is inefficient
B. It is bulky
C. It requires cooling water for its operation
D. None of the above
Answer : C

29. Which of the following statement is correct?
A. The reciprocating compressors are best suited for high pressure and low volume capacity
B. The effect of clearance volume on power consumption is negligible for the same volume of discharge
C. Both (A) and (B)
D. None of these
Answer : C

30. Volumetric efficiency of a compressor without clearance volume
A. Increases with increase in compression ratio
B. Decreases with increase in compression ratio
C. Is not dependent upon compression ratio
D. May increase/decrease depending on compressor capacity
Answer : C

31. The closed cycle in gas turbines
A. Provides greater flexibility
B. Provides lesser flexibility
C. In never used
D. Is used when gas is to be burnt
Answer : A

32. The maximum temperature in a gas turbine is
A. 200°C
B. 500°C
C. 700°C
D. 1000°C
Answer : C

33. Phenomenon of choking in compressor means
A. No flow of air
B. Fixed mass flow rate regardless of pressure ratio
C. Reducing mass flow rate with increase in pressure ratio
D. Increased inclination of chord with air steam
Answer : B

34. Pick up the correct statement
A. Large gas turbines use radial inflow turbines
B. Gas turbines have their blades similar to steam turbine
C. Gas turbine's blade will appear as impulse section at the hub and as a reaction section at tip
D. Gas turbines use both air and liquid cooling
Answer : C

35. Water gas is produced by
A. Carbonisation of coal
B. Passing steam over incandescent coke
C. Passing air and a large amount of steam over waste coal at about 65°C
D. Partial combustion of coal, eke, anthracite coal or charcoal in a mixed air steam blast
Answer : B

36. The pressure of air at the beginning of the compression stroke is ________ the atmospheric pressure.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : B

37. Which is false statement about advantages of multistage compressor in comparison to single stage compressor?
A. Less power requirement
B. Better mechanical balance
C. Less loss of air due to leakage past the cylinder
D. Lower volumetric efficiency
Answer : D

38. High air-fuel ratio in gas turbines
A. Increases power output
B. Improves thermal efficiency
C. Reduces exhaust temperature
D. Do not damage turbine blades
Answer : C

39. The compression ratio in a gas turbine is of the order of
A. 3.5 : 1
B. 5 : 1
C. 8 : 1
D. 12 : 1
Answer : C

40. Euler's equation can be used for
A. Radial flow compressors
B. Axial flow compressors
C. Pumps
D. All of these
Answer : D

41. If p? is the pressure of air entering the L.P, cylinder and p? is the pressure of air leaving the H.P. cylinder, then the ratio of cylinder diameters for a single acting, two stage reciprocating compressor with complete intercooling is given by
A. D?/D? = (p? p?)^1/2
B. D?/D? = (p?/p?)^1/4
C. D?/D? = (p? p?)^1/4
D. D?/D? = (p?/p?)^1/4
Answer : D

42. The thrust on the rotor in a centrifugal compressor is produced by
A. Radial component
B. Axial component
C. Tangential component
D. None of the above
Answer : B

43. The process, which causes the air to enter the impeller blades of a centrifugal compressor at ________ velocity (without effecting the mass of air to flow and velocity of flow) is known as prewhirl.
A. Reduced
B. Increased
C. Zero
D. None of these
Answer : A

44. The ratio of workdone per cycle to the stroke volume of the compressor is known as
A. Compressor capacity
B. Compression ratio
C. Compressor efficiency
D. Mean effective pressure
Answer : D

45. In the aircraft propellers
A. The propulsive matter is caused to flow around the propelled body
B. Propulsive matter is ejected from within the propelled body
C. Its functioning does not depend on presence of air
D. All of the above
Answer : D

46. Pick up the wrong statement
A. Centrifugal compressors deliver practically constant pressure over a considerable range of capacities
B. Axial flow compressors have a substantially constant delivery at variable pressures
C. Centrifugal compressors have a wider stable operating range than axial flow compressors
D. Axial flow compressors are bigger in diameter compared to centrifugal type
Answer : D

47. Isothermal compression efficiency can be attained by running the compressor
A. At very high speed
B. At very slow speed
C. At average speed
D. At zero speed
Answer : B

48. A compressor at high altitude will draw
A. More power
B. Less power
C. Same power
D. More/less power depending on other factors
Answer : B

49. The capacity of a compressor is 5 m /min refers to
A. Standard air
B. Free air
C. Compressed air
D. Compressed air at delivery pressure
Answer : B

50. The assumption made in two stage compression with intercooler is that
A. There is no pressure drop in the intercooler
B. The compression in both the cylinders is polytropic
C. The suction and delivery of air takes place at constant pressure
D. All of the above
Answer : D